The activity of proteolytic enzymes released from damaged pulmonary tissue may produce destruction of pulmonary tissue. The proposed project will compared and contrast the effects on dog lung of aerosolized papain and aerosolized extracts made from leukocyte homogenates, both of which have been reported to produce emphysema-like lesions in animal lung tissue. The release of proteolytic enzymes from leucocytes may produce a less severe emphysema than papain. The effects of exposing the dogs to cigarette smoke for varying periods of time will be studied using both physiologic measurements of blood gases and pulmonary mechanics and scanning electron microscopy as well as standard histologic examination of lung section. In addition, animals which have been treated with papain or leucocyte extract will be exposed to cigarette smoke in order to see if smoking increases the severity of pulmonary damage.